This invention relates generally to semiconductor integrated circuits and more particularly, it relates to a glitch remover circuit for removing glitches and spikes from control signals received on a SCSI (acronym for small computer system interface) bus line that is coupled from a transmission line.
As is generally well known, in order to provide smaller and faster devices in CMOS process technology the sizes of the devices used in the integrated semiconductor circuits have a reduced scaling or a shrinking of the geometries thereof. For example, the gate length of the devices, which have been around 1.6 microns, are further reduced to under 1 micron so as to achieve higher speeds of operation. In particular, when the effective length of the gate decreases the gate delay will be reduced so as to yield faster devices. However, the shrinking of the sizes of the integrated semiconductor devices to a smaller size than the heretofore generally acceptable standard size has not been done without any resulting problems. Such semiconductor devices of reduced dimensions fail generally from being more noise sensitive (i.e., lower noise immunity) and being not capable of providing reliable data transfer.
One application where noise immunity and reliable data transfer becomes important is in the field of data transmission on a fully loaded SCSI bus line which is coupled from a transmission line for communication with small computers. The basic problem encountered when transferring data on the SCSI bus line is due to noise and glitches which may cause double strobing of the data. The glitches are more hazardous when they appear on the REQB and ACKB lines. The control signals REQB and ACKB are used to perform a "handshake" so as to transfer the data back and forth between a target (i.e., disc drive) and an initiator (i.e., host computer). A glitch occurring in the control signal REQB can cause one or more extra bytes to be counted during long data transfers at the transfer rate of between 1.0-10 Mbytes/sec. On the other hand, the incorrect or wrong data could be transferred such as when an early control signal REQB occurs and the data signal lines are still being settled, thus causing the wrong data to be sampled. In another situation, the glitch present in the control signal REQB when the SCSI phase lines are being switched could result in a wrong phase.
Accordingly, there has arisen a need for some type of filtering devices which can remove the glitches and spikes occurring in the control signals REQB and ACKB on the SCSI bus line so as to provide reliable and accurate data transmission.